Acoustical and thermal liners for application to vehicles are well known in the art. These liners typically rely upon both sound absorption, i.e. the ability to absorb incident sound waves and transmission loss, i.e. the ability to reflect incident sound waves, in order to provide sound attenuation. They also rely upon thermal shielding properties to prevent or reduce the transmission of heat from various heat sources (e.g. engine, transmission and exhaust system), to the passenger compartment of the vehicle. Such insulation is commonly employed as a hoodliner, dash liner and firewall liner. More recently, such liners have been employed on engine covers so as to attenuate the sound of the engine closer to its source.
Examples of acoustical and thermal insulation in the form of liners are disclosed in a number of prior art patents including U.S. Pat. No. 4,851,283 to Holtrop et al. and U.S. Pat. No. 6,008,149 to Copperwheat. As should be apparent from a review of these two patents, engineers have generally found it necessary to construct such liners from a laminate incorporating (a) one or more layers to provide the desired acoustical and thermal insulating properties and (b) one or more additional layers to provide the desire mechanical strength properties which allow simple and convenient installation as well as proper functional performance over a long service life.
While a number of adhesives, adhesive webs and binding fibers have been specifically developed over the years to secure the various layers of the laminates together, laminated liners and insulators have an inherent risk of delamination and failure. The potential is, in fact , significant mainly due to the harsh operating environment to which such liners and insulators are subjected. Many liners and insulators are located near and/or are designed to shield high heat sources such as the engine, transmission and components of the exhaust system. As a result, the liners and insulators are often subjected to temperatures in excess of 200 F which have a tendency to degrade the adhesives or binders over time.
Additionally, many liners and insulators are subjected to water from the surface of the roadways which has a tendency to be drawn by capillary action into the interface between the layers of the liners or insulators. Such water may have a deleterious effect upon the integrity of the adhesive layer over time. This is particularly evident when one considers that water may also include in solution salt or other chemicals from the roadway, which are corrosive and destructive.
A need is therefore identified for a hood, dash, firewall or engine cover liner incorporating a nonlaminate acoustical and thermal insulating layer of polymer fibers which avoids any inherent potential for delamination. Such a liner is suitable for use in the high temperature operating environment of the engine compartment and capable of providing the desired mechanical strength and rigidity for ease of installation as well as the desired acoustical and thermal insulating properties.